Fuel cell system for producing electrical energy

ABSTRACT

A fuel cell system has a fuel cell disposed within a fuel cell enclosure for electrochemically combining externally supplied oxygen with hydrogen to produce direct-current electrical energy and water as a reaction product. A hydrogen-containing fuel such as a chemical hydride contained within a fuel container receives the by-product water and reacts therewith to produce hydrogen, which is supplied to the fuel cell to sustain operation thereof without need of adding externally supplied hydrogen. The integration of the supply of hydrogen with the fuel cell results in a weight and volume reduction as well as internal chemical control of the production of hydrogen to sustain the electrical power generation and internal water management whereby liquid water emission is substantially reduced.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 10/273,280 filedOct. 17, 2002 now U.S. Pat. No. 6,864,022, which claims the benefit ofU.S. Provisional Application No. 60/330,275 filed Oct. 19, 2001, andpriority thereto for common subject matter is hereby claimed.

BACKGROUND OF THE INVENTION

The present invention relates generally to fuel cells, and moreparticularly, to fuel cells that consume gaseous hydrogen-containingfuels and produce electrical energy and water.

Typically, such a fuel cell generates water in the normal course ofpower generation using oxygen in the air to electrochemically combinewith hydrogen gas to produce electrical energy by well-knownelectrochemical principles. Advantageous fuel cells for energyconversion are described in my U.S. Pat. Nos. 4,863,813; Re34,248;4,988,582 and 5,094,928. In a fuel cell of the type described therein, ahydrogen-containing material at room temperature, such as a gaseousmixture of hydrogen and oxygen, is directly converted to direct-currentelectrical energy and the only reaction product is water.

In one such specific illustrative fuel cell, a submicrometer-thick gaspermeable ionically conducting electrolytic membrane made ofpseudoboehmite is deposited on an electrode that comprises a platinizedimpermeable substrate. A layer of platinum, for example, is deposited onthe top surface of the membrane to form the other electrode of the fuelcell, which electrode is porous enough to allow the gas mixture to passinto the membrane. In a hydrogen/air mixture, such a fuel cell providesuseful current at an output voltage as large as about one volt. Whilethe voltage and current provided by the basic fuel cell are adequate formany applications of practical interest, I recognized that it would bedesirable to devise a compact source of hydrogen for this and other fuelcells especially for portable electronic device applications, such aslaptop computers and mobile phones. A suitable combination of a fuelcell with a lightweight, low volume source of hydrogen, could provide animproved source of power for portable electronic applications comparedwith batteries.

Several chemical hydride materials, with a high hydrogen content, reactwith water to yield hydrogen. The combined weight and volume of achemical hydride and the water necessary to react with it to makehydrogen for use in a fuel cell, is termed the “specific energy” contentof the fuel, which is normally measured in terms of Watt-hours (energycontent) divided by the weight or volume of the chemical hydride plusits needed reactant water. Hence Watt-hours per kilogram or Watt-hoursper liter are examples of the specific energy of a fuel for a fuel cell.In a portable application, a fuel cell with its fuel, termed a fuel cellsystem, would benefit from the use of a high specific energy fuel whichwould thereby reduce the carrying weight and volume of the fuel cellsystem.

I recognized that since a fuel cell produces water as a by-productduring the normal course of its power-generating operation, a fuel cellthat can use this by-product water as the reactant with a chemicalhydride fuel would be advantageous in raising the specific energy of afuel cell system by eliminating the need to carry additional water. Onlyone reactant, the chemical hydride, would then need to be carried in thefuel cell system. I recognized that fuel cells that could tolerate airmixed with their fuel supply would particularly benefit from such amethod of generating hydrogen. I also recognized that a chemical meansof control of the rate of hydrogen generation in such a fuel cell systemwould be advantageous. I further recognized that a portable fuel cellsystem would benefit from a means to collect the water produced duringnormal production of electrical energy to avoid wetness and flooding inthe vicinity of the operating fuel cell.

SUMMARY OF THE INVENTION

The present invention implements operation of a fuel cell with hydrogenfuel derived from the reaction of a chemical fuel, such as a chemicalhydride, with the by-product water from the fuel cell. Integration ofthis fueling means with a suitable fuel cell constitutes a device,termed a fuel cell system, which is characterized in that it onlyrequires an external supply of oxygen or air and has a higher specificenergy density than a fuel cell system that requires a separate oradditional source of water. By internally utilizing the fuel cell's ownwater output, the present invention improves the performance, controland safety of a fuel cell system in which a fuel cell is coupled to thefuel supply consistent with the principles of the invention. Theimproved performance of the device is characterized by a higher specificenergy content, as measured by weight and volume. This improvement isachieved by elimination of the need to include additional water forreaction with a chemical hydride to produce hydrogen.

An additional advantage of the present invention is that it controls therate of hydrogen generation by controlling the water supply to thechemical hydride. The water supply available for reaction with thechemical fuel containing hydrogen is controlled by the electrical energydemanded. In the present invention, a fuel cell that produces watervapor during the course of its operation is coupled to a suitablechemical hydride, which is defined as a hydrogen-containing fuel thatreacts with water vapor to produce hydrogen gas under the same ambientconditions as the fuel cell and does not need a separate source of waterother than supplied by the fuel cell. In the present invention, thewater vapor from the fuel cell exhaust is directed towards a containercontaining the suitable chemical hydride material where it reacts toform hydrogen, which is then delivered to the anode of a fuel cell tosustain the electrical energy production.

Typical fuel cells, however, produce water at the cathode or positiveelectrode which is mixed with air and so the product after reaction ofthis typical fuel cell exhaust with a chemical hydride would containboth hydrogen and air. In these typical fuel cell designs, the fuel isrequired to be mostly uncontaminated with air. Therefore if the fuelcell requires hydrogen mostly unmixed with air at its anode or negativeelectrode, an additional means to separate the water vapor from the airor the hydrogen from the air would be advantageous, so that onlyhydrogen mostly unmixed with air is supplied to the fuel cell anode.

Advantageously, a fuel cell which not only produces water vapor but alsorequires a mixture of air and hydrogen to generate electrical energy,would especially benefit from the present invention since no separationof water from air or hydrogen from air would be required to operate sucha fuel cell. Examples of such a fuel cell are described in my U.S. Pat.Nos. 4,863,813; Re34,248; 4,988,582 and 5,094,928. This fuel cellcombined with the present invention would constitute a preferredembodiment. Another fuel cell that would advantageously benefit from thepresent invention would be a fuel cell that produces water unmixed withair, for instance a fuel cell which produces water at the anode, ornegative electrode side of the cell, where it is accompanied by mostlyhydrogen, an example being the solid oxide fuel cell.

Since a fuel cell produces by-product water in direct proportion to theamount of electrical energy produced, the supply of water in the presentinvention is regulated by the electrical energy demand. In the presentinvention, the chemical fuel such as a chemical hydride is preferablychosen to require the same amount of reactant water as the fuel cellproduces to sustain the fuel cell operation. This then preventsexcessive and wasteful production of hydrogen and thereby acts as acontrol, which is advantageous to both conservation of the remainingchemical hydride material and to safety. The chemical hydride is alsopreferably selected on the basis that the supply of water by the fuelcell is sufficient to react all of the chemical hydride. For a givenamount of electrical energy produced, the rate of production of hydrogenneeded for use in a fuel cell is exactly balanced by the amount of waterit produces when using a preferable chemical hydride. As the electricalenergy demand is increased, more current is produced accompanied by morewater production, which on reaction with the chemical hydride leads tomore hydrogen production to sustain the higher electrical energy demand.As the demand for electrical energy is reduced to zero, the amount ofwater produced is correspondingly reduced to zero and as a consequence,the amount of hydrogen is also reduced to zero, which provides a safemethod of storing and transporting hydrogen. Thereby, the presentinvention advantageously provides a means of efficient and safe controlof the amount of hydrogen produced.

Another advantage of the present invention would be the use of a solidhydrogen-containing fuel that effectively absorbs product water from thefuel cell, thereby avoiding wetness and flooding in the vicinity of theoutlet from an operating fuel cell. Several inorganic chemical hydridesreact with water vapor to give hydrogen and also produce a solidproduct, which is a beneficial method of “water management” in thepresent invention. Further attendant benefits characterize the presentinvention since it provides a means of measuring the remaining energycontent of the fuel. For fuel cells using the present invention, theproduction of hydrogen may be accompanied by a weight and volume gainwithin the chemical hydride container. Such physical changes could bemonitored by simple gravimetric or volumetric means to provide a measureof the extent of reaction undergone by the chemical hydride andtherefore the remaining energy content of the system.

The foregoing as well as other objects, features and advantages of thepresent invention will become readily apparent to those of ordinaryskill in the art upon a reading of the following detailed description ofthe invention when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagrammatic representation of one embodiment ofa fuel cell system according to the principles of the present invention;

FIG. 2 is an explanatory diagram showing the reactions that take placeusing air as the source of oxygen during operation of the fuel cellsystem shown in FIG. 1; and

FIG. 3 is a simplified diagrammatic representation of another embodimentof a fuel cell system according to the principles of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION Fuel Cell Integrated with FuelSupply

An illustrative example of a fuel cell system according to the presentinvention is shown in FIG. 1. The fuel cell system comprises ahydrogen-containing fuel 1 such as, for example, a NaBH₄ chemicalhydride fuel, housed within a fuel container 2. The fuel container 2 hasan inlet 3 for admitting water principally in the form of water vaporinto the container 2 for reaction with the hydrogen-containing fuel 1 toproduce hydrogen gas which exits the container 1 through an outlet 4.

A fuel cell enclosure 5 has disposed therein a fuel cell 6 which may,for example, be of the type described in my U.S. Pat. Nos. 4,863,813;Re43,248; 4,988,582 and 5,094,928, the entire disclosures of whichconstitute part of the disclosure of the present application and arehereby incorporated by reference herein. An example of one such fuelcell 6 is shown diagrammatically in FIG. 1 and comprises a mixed-gasfuel cell having an impermeable substrate 18, an impermeable orpermeable catalytic electrode 17, a permeable ion-conductingelectron-insulating electrolytic membrane 16 (referred to as a solidelectrolyte body in my earlier patents) and a permeable catalyticelectrode 15. The catalytic electrodes 15 and 17 and the membrane 16 aretypically thin in accordance with the prior said disclosures from whichthe term thin film fuel cell used in conjunction with these disclosuresderives. By contrast, the substrate 18 is typically relatively thickwhen compared with the thin film fuel cell since it acts as a mechanicalsupport for the thin film fuel cell. Substrate 18 may usefully also beelectronically conductive. The fuel cell 6 is provided with a pair oflead wires 6 a,6 b for extracting the electrical energy produced by thefuel cell, and the lead wires 6 a,6 b are connected to fuel cellelectrodes in a manner known in the art. The fuel cell enclosure 5 isprovided with an oxygen inlet 7 for introducing oxygen into theenclosure, a hydrogen inlet 8 for introducing hydrogen gas into theenclosure, and a water outlet 9 for discharging water from theenclosure. An inlet valve 10 is preferably provided at the oxygen inlet7 for controlling the inflow of oxygen gas.

In the embodiment shown in FIG. 1, the outlet 4 of the fuel container 2is directly connected to the hydrogen inlet 8 of the enclosure 5 by apassage such as a conduit 11. In this manner, the interior of the fuelcontainer 2 communicates with the interior of the fuel cell enclosure 5so that hydrogen gas produced by the fuel 1 discharges through theoutlet 4 and is directed through the conduit 11 and the hydrogen inlet 8into the fuel cell enclosure 5. In this embodiment, another passage suchas a conduit 12 communicates the water outlet 9 of the fuel cellenclosure 5 with the inlet 3 of the fuel container 2. This enables waterproduced during operation of the fuel cell 6 to be admitted into thefuel container 2 for reaction with the hydrogen-containing fuel 1. Ifnecessary, a venting valve 14 may be provided along the conduit 12.

In operation, oxygen or air is admitted through the inlet valve 10(which is in the open position) and the oxygen inlet 7 into the fuelcell enclosure 5 and mixes with hydrogen admitted through the hydrogeninlet 8 to form the gas mixture needed for the fuel cell 6 to generateelectrical energy which passes along the lead wires 6 a,6 b attached tothe fuel cell electrodes. A corresponding amount of water vapor isgenerated by the fuel cell 6 and is discharged from the fuel cellenclosure 5 through the water outlet 9 and passes through the conduit 12to the hydrogen-containing fuel 1 via the inlet 3. The water vaporreacts with the hydrogen-containing fuel 1 in the fuel container 2, andresults in more hydrogen being passed to the fuel cell 6 to sustain theelectrical energy generation.

While the primary purposes of the inlets 7 and 8 and outlet 9 are toallow passage of the primary fuel cell reactants oxygen and hydrogen andthe product water, respectively, in practice other gases may accompanythe primary reactants and product water. For instance, in addition towater, gases not reacted by the fuel cell 6 including unreacted oxygenand hydrogen may pass through the outlet 9 and then pass unreactedthrough the fuel 1, container 2, outlet 4 conduit 11 and inlet 8 to theenclosure 5. If air is used as the source of oxygen, nitrogen will alsopass unreacted through the elements of the fuel cell system shown inFIG. 1 and further illustrated in FIG. 2. Such air will subsequentlybecome oxygen depleted as a result of normal fuel cell operation.

To maintain a directed flow pattern, oxygen or air may be forced intothe fuel cell enclosure 5 through the oxygen inlet 7 with the inletvalve 10 open. This may be achieved by using some of the electricalenergy produced by the fuel cell 6. The venting valve 14 may need to beincorporated to allow oxygen-depleted air from the fuel cell container 2to be removed and replaced by oxygen-rich air through the oxygen inlet7.

In the embodiment shown in FIG. 3, the valves 10 and 14 together withthe outlet 4, the inlet 8 and the conduits 11 and 12 are eliminated, andthe fuel cell enclosure 5 is directly connected to the fuel container 2.One or more openings (such as the outlet 9) provided in the fuel cellenclosure 5 are aligned with one or more similar openings (such as theinlet 3) provided in the fuel container 2 so that air diffusing throughthe oxygen inlet 7 mixes with hydrogen diffusing from the fuel container2 to provide the mixed gas environment required for power generation bythe fuel cell 6, and water vapor diffusing from the fuel cell enclosure5 enters the fuel container 2 for reaction with the hydrogen-containingfuel 1. This embodiment would allow a simpler design and would generatelower levels of power and be suitable for low powered portable equipmentsuch as a cellphone. Higher levels of power, such as may be requiredduring cellphone transmission, would be supplied by an energy storagedevice such as a small battery, kept constantly charged by the low powerfuel cell system.

In accordance with another aspect of the present invention, the fuelcontainer 2 is removably connected in the fuel cell system so that itcan be removed and replaced by a new fuel container. For this purpose,any suitable removable connection may be employed, such as, for example,threaded connections or bolted flange connections, to removably connectthe inlet 3 and the outlet 4 of the fuel container 2 to the conduits 11and 12. In the embodiment shown in FIG. 3, the outlet 4, the inlet 8 andthe conduits 11 and 12 are dispensed with, and the fuel container 2 isremovably connected directly to the fuel cell enclosure 5 so that theoutlet 9 of the fuel cell enclosure 5 communicates directly with theinlet 3 of the fuel container 2 through a series of aligned openings.Alternatively, the conduit 12 could be retained, in which case only theinlet 3 of the fuel container 2 need be removably connected to theconduit 12. In this manner, a spent fuel container 2 may be removed andreplaced with a fresh fuel container.

The sequence of reactions involved in the fuel cell system of FIG. 1 areshown as a gas flow chart in FIG. 2:

-   At the fuel cell 6: 4H₂+2O₂ (air)=>4H₂O (+electrical energy)-   In the fuel container 2: NaBH₄+4H₂O=>4H₂+NaOH.B(OH)₃-   Overall Reaction: NaBH₄+2O₂ (air)=>NaOH.B(OH)₃

The overall reaction shows that the fuel cell system shown in FIG. 1produces electrical energy from only one external reactant (oxygen),which is readily available in air, and that no excess hydrogen isproduced other than is needed internally for electrical energyproduction. The reaction also shows that the amount of water produced bythe fuel cell is sufficient to react all of the chemical hydridematerial. An internal cycle of water and hydrogen production is directlycontrolled and regulated by the external demand for electrical energywhich makes the system inherently safe. This cycle may be characterizedas follows: For a given amount of electrical energy produced, the rateof production of hydrogen needed for use in a fuel cell is exactlybalanced by the amount of water it produces when using suitable chemicalhydrides. As the demand for electrical energy is increased, more currentis produced accompanied by more water production, which leads to morehydrogen production to sustain the higher electrical energy demand. Asthe demand for electrical energy is reduced to zero, the amount of waterproduced is correspondingly reduced to zero and as a consequence theamount of hydrogen is also reduced to zero, which makes the system safefor storing and transporting hydrogen with the inlet valve 10 closed.

A fuel cell capable of producing electrical power on exposure to amixture of air and 2–4% hydrogen, such as described in U.S. Pat. Nos.4,863,813; Re43,248; 4,988,582 and 5,094,928, would particularly benefitfrom the present invention since the carrying capacity of air for watervapor is in the same range, namely 2–4% for the temperature range 20–30°C. This particular benefit arises because in the exemplary reactionsshown above, reaction of a given number of water molecules with thechemical hydride produces the same number of molecules of hydrogen thusproviding a natural control of the amount of hydrogen generated to therange 2–4% which is generally considered to be a safe level of hydrogenin air, which would be especially beneficial for use in the portableelectronic device applications envisaged such as mobile phones andlaptop computers. In addition, the supply of water as vapor is anadvantageous means to utilize most efficiently the chemical hydridefuel.

The inlet valve 10 prevents uncontrolled access of air or oxygen to thefuel cell system when not in use as shown in FIG. 1. The inlet valve 10would typically comprise a shut-off valve, mechanically or electricallyactivated when the fuel cell 6 was no longer delivering power. Theventing valve 14 would also be closed when the fuel cell 6 was notoperating to produce electrical power.

The present invention couples the fuel cell to the chemical fuel by asystem of inlets and outlets which obviate the need for supplyingexternal water to react with the chemical hydride. The fuel cell systemof the present invention thereby is lighter in weight and smaller involume by the amount of water that is not needed, which for sodiumborohydride, amounts to a weight and volume savings of approximately twothirds. This is clearly advantageous for portable applications. Thespecific energy density based on the hydrogen content of sodiumborohydride alone (without including the volume or weight of reactantwater) is approximately 6300 Watt-hours per liter and 5900 Watt-hoursper kilogram. Other chemical hydrides would provide even higher energydensities if used in accordance with the present invention.

Fuels

Several suitable inorganic chemical hydrides react with water in abalanced manner to benefit this invention and give hydrogen, andexamples of such reactions are given below.NaBH₄+4H₂O=>4H₂+NaOH.B(OH)₃NaBH₄+4H₂O=>4H₂+NaBO₂.2H₂OCaH₂+2H₂O=>2H₂+Ca(OH)₂LiBH₄+4H₂O=>4H₂+LiOH.B(OH)₃LiAlH₄+4H₂O=>4H₂+LiOH.Al(OH)₃

These are examples of suitable fuels for beneficial use in the presentinvention. Their selection will also depend upon factors including theirspecific energy density, rate of reaction with water vapor, completenessof reaction with water vapor, temperature, etc. Substantially higherspecific energy densities are available by using a Li-based hydride suchas LiBH₄, which has an energy density of approximately 10,000 Watt-hoursper liter and per kilogram. If used in the present invention, thisspecific energy is much higher than popular fuels for fuel cells such asmethanol and relatively heavy metal hydrides which adsorb and desorbhydrogen gas as opposed to chemical hydride fuels used in the presentinvention which react with water to produce hydrogen gas.

Advantageous embodiments of the present invention would include means toutilize as much of the chemical hydride fuel as possible by the fuelcell supplied water vapor. The water supplied from the fuel cell to thechemical hydride, if in a vaporized state, would assist penetration intoa solid chemical hydride mass to achieve a more uniform extent ofreaction of the available solid chemical hydride (high utilization) thanif the water were in a liquid state. In particular, water as vapor,reduces the onset of vapor-pathway blockage of the solid chemicalhydride particulate mass, which would otherwise reduce system energydensity by precluding further water access to the inner particles ofchemical hydride.

Mixing of the particles of chemical hydride with inert material thatpromotes ingress and penetration by water vapor may be advantageous.Judicious choice of chemical hydride particle size and particle sizedistribution may also be advantageous to high utilization. Increasingthe porosity of the chemical hydride fuel towards water vapor could beachieved by making the chemical hydride into a sheet or wafer form andstacking the sheets or wafers one atop another with an air spacetherebetween to allow easy ingress of water vapor to facilitate a higherdegree and uniformity of reaction of the chemical hydride. The rate ofreaction of the solid chemical hydride fuel may be raised by includingadditives in the chemical hydride such as a catalyst for the reactionincluding addition of ruthenium or acid-containing compounds.

The addition of a fusible polymer to the chemical hydride particles maybe beneficial for safety by selecting a polymer which would melt andspread over the remaining chemical hydride fuel if the temperature roseto an unacceptable level, which would present a barrier to furtherreaction with incoming water vapor thereby reducing the rate of reactionof the water vapor with the chemical hydride fuel.

While it is anticipated that the principal source of hydrogen is byreaction of the hydrogen-containing fuel with water, as this fuelbecomes progressively so reacted, the rate of production of hydrogen maydiminish and the fuel cell may require a supplemental hydrogen supply tomaintain undiminished power output.

Water Management and Disposal

All fuel cells producing electrical energy from hydrogen and oxygengenerate water which at ambient temperature can condense and accumulateat their electrodes and so reduce electrode performance by obstructingthe flow of reactant gas to the catalytic surfaces of the electrode.This is commonly prevented by increasing airflow to displace the water.The present invention removes water vapor without having to increaseairflow and internally reduces water condensate formation by acting as a‘drying’ agent in close proximity to the fuel cell. This is especiallyadvantageous in fuel cell applications near to people and equipment,which are susceptible to build up of moisture.

The present invention anticipates the removal of both the spent chemicalhydride fuel (fuel reaction product) with chemically reacted water bymechanical means. Removal of the fuel container 2 in FIG. 1 andreplacement by a container with unreacted chemical hydride can bedesigned to be simple and efficient. Disposal of the spent sodiumborohydride which may contain solid borax is not anticipated to beproblematic for this invention.

While the preferred embodiments of the present invention have beendescribed with reference to mixed-gas fuel cells, it is understood thatthe invention is not so limited and can be carried out using generallyany type of fuel cell that consumes hydrogen and produces water as areaction product. For example, the present invention can be practicedusing fuel cells that require different electrochemical reactants ordifferent electrochemical reactant concentrations at the cathode andanode electrodes provided that the fuel cells consume hydrogen andproduce water as a reaction product.

While the present invention has been described with reference topresently preferred embodiments thereof, other embodiments as well asobvious variations and modifications to all the embodiments will bereadily apparent to those of ordinary skill in the art. The presentinvention is intended to cover all such embodiments, variations andmodifications that fall within the spirit and scope of the appendedclaims.

1. A fuel cell system for producing direct-current electrical energy,comprising: an enclosure having an oxygen inlet, a hydrogen inlet and awater outlet; a mixed-gas fuel cell disposed within the enclosure forelectrochemically combining oxygen gas introduced through the oxygeninlet with hydrogen gas introduced through the hydrogen inlet to producedirect-current electrical energy and water as a reaction product; ahydrogen-containing fuel in communication with the water outlet forreceiving the water and any unreacted gases exiting the enclosure andreacting with the water to produce hydrogen gas; and a passage fordirecting the hydrogen gas produced by the hydrogen-containing fuel andany unreacted gases mixed therewith through the hydrogen inlet into theenclosure wherein the hydrogen gas mixes with the oxygen gas to producea hydrogen-lean mixed-gas fuel to sustain operation of the fuel cell. 2.A fuel cell system according to claim 1; further including a fuelcontainer containing therein the hydrogen-containing fuel, the fuelcontainer having an inlet in communication with the water outlet and anoutlet in communication with the passage.
 3. A fuel cell systemaccording to claim 2; wherein the fuel container is removable from thefuel cell system and replaceable with another fuel container containinghydrogen-containing fuel.
 4. A fuel cell system according to claim 3;wherein the fuel container is removably connected to the enclosure.
 5. Afuel cell system according to claim 2; further including another passageinterconnecting the water outlet of the enclosure with the inlet of thefuel container.
 6. A fuel cell system according to claim 5; furtherincluding a venting valve disposed along the other passage.
 7. A fuelcell system according to claim 6; further including an inlet valve forcontrolling the introduction of oxygen gas through the oxygen inlet. 8.A fuel cell system according to claim 5; wherein the other passage, inthe region where it connects to the inlet of the fuel container, is freeof any obstruction that would restrict or impede the free flow of waterthrough the inlet into the fuel container.
 9. A fuel cell systemaccording to claim 1; further including an inlet valve for controllingthe introduction of oxygen gas through the oxygen inlet.
 10. A fuel cellsystem according to claim 1; wherein the hydrogen-containing fuel is achemical hydride.
 11. A fuel cell system according to claim 10; whereinthe chemical hydride is selected from the group consisting of NaBH₄,CaH₂, LiBH₄ and LiAlH₄.
 12. A fuel cell system according to claim 1;wherein the fuel cell comprises a thin film fuel cell.
 13. A fuel cellsystem according to claim 1; wherein the hydrogen-containing fuelincludes one or more additives to raise or lower the rate of reaction ofthe hydrogen-containing fuel with water.
 14. A fuel cell systemaccording to claim 13; wherein one of the additives absorbs heat.
 15. Afuel cell system according to claim 13; wherein one of the additives isa fusible polymer.
 16. A fuel cell system according to claim 1; whereinthe hydrogen-containing fuel is a solid hydrogen-containing fuel.
 17. Afuel cell system according to claim 1; wherein the hydrogen-containingfuel is a solid hydrogen-containing fuel that reacts with the water toproduce hydrogen gas and a solid spent fuel reaction product.
 18. A fuelcell system according to claim 17; wherein the solid hydrogen-containingfuel is comprised of solid particles.
 19. A fuel cell system accordingto claim 18; wherein the solid particles are compacted into sheets. 20.A fuel cell system according to claim 19; wherein the sheets are stackedone atop another with a space between adjacent sheets.
 21. A fuel cellsystem according to claim 18; wherein the solid particles are mixed withan inert material.
 22. A fuel cell system according to claim 1; whereinthe solid hydrogen-containing fuel is selected to produce a solid spentfuel reaction product that acts as a drying agent effective to reduceformation of water condensate.
 23. A fuel cell system according to claim1; wherein the water outlet communicates directly with thehydrogen-containing fuel so that the water exiting the enclosure passesdirectly to the hydrogen-containing fuel.
 24. A fuel cell systemaccording to claim 1; wherein the water exiting the enclosure passesdirectly to the hydrogen-containing fuel without separation of the waterfrom any other components exiting the enclosure.
 25. A fuel cell systemaccording to claim 1; wherein the water produced by operating the fuelcell is primarily in the form of water vapor; and thehydrogen-containing fuel reacts with the water vapor to produce hydrogengas.
 26. A fuel cell system for producing direct-current electricalenergy, comprising: an enclosure having an oxygen inlet; a fuel celldisposed within the enclosure for electrochemically combining oxygen gasintroduced through the oxygen inlet mixed with hydrogen gas to producedirect-current electrical energy and water as a reaction product; and afuel container containing a hydrogen-containing fuel that reacts withwater to produce hydrogen gas; wherein the enclosure and the fuelcontainer each have one or more openings, the one or more openings ofthe enclosure communicating directly with the one or more openings ofthe fuel container to pass water from the enclosure directly to the fuelcontainer and to pass hydrogen gas from the fuel container directly tothe enclosure to produce a hydrogen-lean mixed-gas fuel within theenclosure to sustain operation of the fuel cell.
 27. A fuel cell systemaccording to claim 26; wherein the fuel container is removably connectedto the enclosure to enable removal of a spent fuel container andreplacement thereof with a fresh fuel container.
 28. A fuel cell systemfor producing direct-current electrical energy, comprising: an enclosurehaving an oxygen inlet, a hydrogen inlet and a water outlet; a mixed-gasfuel cell disposed within the enclosure for electrochemically combiningoxygen gas introduced through the oxygen inlet with hydrogen gasintroduced through the hydrogen inlet to produce direct-currentelectrical energy and water as a reaction product; a fuel containerhaving an inlet connected to the water outlet for admitting the waterand any unreacted gases exiting the enclosure into the fuel container; ahydrogen-containing fuel disposed in the fuel container for reactingwith the water to produce hydrogen gas; and a passage connecting anoutlet of the fuel container to the hydrogen inlet for directing thehydrogen gas and any unreacted gases exiting the fuel container into theenclosure wherein the hydrogen gas mixes with the oxygen gas to producea hydrogen-lean mixed-gas fuel to sustain operation of the fuel cell.